Method of and apparatus for making seamless tubes



Sept. 12, 1933. H. c. INSLEE 1,926,237

METHOD OF AND APPARATUS FOR MAKING SEAMLESS TUBES Filed June 30, 1928 3 Sheets-Sheet l :2 gFN 20R BY WWW ATTOR N EY Sept. 12, 1933. H. c. INSLEE 1,926,237

METHOD OF AND APPARATUS FOR MAKING SEAMLESS TUBES I Filed June 30, 1928 3 Sheets-Sheet 2 l VENT R %Al'4.M

' ATTORNEYS.

Sept. 12, 1933. H. c. INSLEE 1,926,237

METHOD OF AND APPARATUS FOR MAKING SEAMLESS TUBES Filed June so, 1928 3 Sheets-Sheet 5 ATTORNEYS.

Patented Sept. 12, 1933 UNITED. STATES METHOD OF AND APPARATUS F0 MAKING SEAMLESS TUBES Heber- C. Inslee, New York, N. Y., assignor to The Babcock & Wilcox Tube Company, West Mayfield, Pa., a corporation of Pennsylvania Application June 30, 1928. Serial No. 289,581

10 Claims.

This invention relates to the making of seamless tubes. The invention comprises improvements in the known method of making seamless metal tubes by compressing and cross-rolling a heated round metal bar, or billet, and advancing the metal over a piercing point or mandrel, and in piercing mills for so making such tubes.

The invention aims to improve the operation of such piercing mills, and especially to increase the efliciency of the mill and to improve the quality of the product, and aims, further, to provide a piercing mill which shall be more convenient to operate than the piercing mills heretofore used.

Heretofore it has been the practice to drive the two or more conicalrolls, barrel rolls, discs or other rolls of cross-rolling piercing mills at the same speed, and the rolls have usually been geared together. I have found that under actual conditions of operation it is frequently not only unnecessary, but undesirable, to have the rolls driven at the same speed, and that the eificiency of the mill may be increasedand the quality of the product improved by driving the rolls at different speeds.

While the highest efficiency of across-rolling piercing mill is theoretically obtained when the rolls are rotating at the same surface speed and doing the same work, this is not often the condl-.

tion in actual practice. Usually the power a! sorbed and delivered by the individual rolls will difier more or less, and when this difference, which, unless due to a difference in diameter of the rolls, generally results from a difference in slip due to difference in smoothness of the rolls,

is considerable, it causesa marked decrease in the efliciency of the mill, or rate of output for power consumed. It also affects the quality of the product. I have found that such a condition of different degrees of smoothness of the rolls may be compensated for to at least a very considerable degree by increasing the speed of the smoother roll. If one of two rolls driven at the same speed is slipping on the work more than another because of its having a smoother or otherwise diiferent surface, it will require less driving torque and take less power than such other roll and do less than its proportionate share of the work. If, under this condition, the speed of the smoother roll be increased, the power which it absorbs and delivers is increased and the speed of travel of the billet is increased without corresponding increase of total power consumed by the millzthat is, the efiiciency of the mill is increased. Also, the quality of the product is improved.

So, also, a difference in work' done by the in dividual rolls due to a difference in diameter of the rolls, the surface of the rolls being alike, will put the mill out of balance and decrease its cfiiciency and affect the quality of the product,

and this condition may also be corrected by relative speed adjustment of the rolls.

When one of the rolls of a two-roll piercing mill having the usual guides for the billet as it" passes between the rolls is smoother than the for the eccentricity of the product when operat;

ing under such conditions. Such inequality of pressure ofthe billet on the guides is reduced by the adjustment of the relative speed ofthe rolls in the direction the rolls.

Therefore; instead of driving the rolls of the piercing mill at equal speed, the relative speed of the rolls is, according to the present invention, adjusted in the direction of equalization of power exerted, or work done, by the rolls. -When of equalization of work done by the work being done by the individual rolls is measured by the resistance torque, or load on the driving means, the speed adjustment is made according to the load readings in the direction of equality of load.

While it is true that, even if the speed of a slipping relatively smooth roll is increased to make-the load on the driving means of this roll equal to that on the driving means of a roll which is notslipping or which is slipping less, the work doneby the smooth roll may not be increased to such extent as to fully equal that done by. the non-slipping roll, yet the difference in work done will be reduced, and the performance of the machine improved. The work done, or power delivered, by the rolls will be equalized to a degree, that is, the adjustment will be in the direction of equalization of work done, or,'in other words, will be such as to reduce the difference in work done by the individual rolls.

Speed adjustment of the rolls according to the invention has the further advantage that, by avoiding or lessening the harmful effect on the efficiency of the mill and the quality of the product of a difference in diameter of the rolls or a difference in the character or finish of the roll surfaces, or both, the necessity of frequent machining of the rolls to correct inequality of size and finish is avoided.

In a piercing mill according to the present invention and for practicing the method forming part of the invention, a separate independent motor is most desirably provided for driving each of the rolls, and for each driving motor there is provided a load indicator and speed controlling means, so that the relative speeds of the rolls may be controlled to proportion the loads on the motors in any desiredratio, and especially so that the loads on the individual motors may be equalized or adjusted in the direction of equalization. By this means, the load on each motor may be observed and the desired adjustment of relative speed and power delivered to the individual rolls, and, therefore, of power exerted by or work done by the individual rolls, may be made while the mill is in operation. The speed of the rolls may be controlled manually, or at will, or the speed adjustment may be automatic, or both automatic and manual control may be employed.

Electric motors are most desirablyused, and ammeters, one in the circuit of each motor, may

. be used as load indicators. If manual control of the speed of the rolls is to be depended on alone, straight shunt wound direct current motors which will hold their speed approximately constant for any adjustment of the speed controlling means are best employed; It is most desirable,

however, to provide for a degree of automatic speed control, and this result may be secured by using compound wound direct current motors having a considerable drooping speed-torque characteristic. With such a motor, as the load on the motor decreases, the speed increases, so that the power delivered by the motor is maintained more nearly constant than in the case of the straight shunt motor, the degree to which the power is maintained depending on the degree of speed-torque droop of the motor. When such motors are used for driving the rolls, the power delivered to the individual rolls will be automatically adjusted to compensate, at least in part, for difference in slip due to difference in the condition of the roll surfaces and for a difference in roll size. For best results, means should be provided for varying the speed of the rolls manually in addition to the automatic speed control resulting from the use of compound wound motors.

A further feature of the invention consists in connecting the individual driving motors directly to the roll shafts. This is desirable because of the reduction in friction losses, and is made possible by using small rolls driven at a relatively high speed, so that the rolls may be driven by direct-connected electric motors without having to use motors of prohibitive size and weight in order to provide the necessary power.

Other features and advantages of the invention will appear from the following detailed description.

A full understanding of the invention can best be given by a detailed description of an approved construction embodying the apparatus features of the invention and adapted for practicing the method; and such a description will now be given in connection with the accompanying drawings illustrating a two roll piercing mill having conical rolls. In said drawings:

Fig. 1 is a plan view of the mill;

Fig. 2 is an elevation of one side of the mill;

Fig. 3 is a detail sectional view taken on line 33 of Fig. 1; and

Fig. 4 is a wiring diagram indicating the two motors and showing the speed controlling and load indicating means.

Referring to the drawings, the piercing mill illustrated is of the cone roll type having two conical rolls 10 and 11 mounted with their axes at an angle of 30 from the center line of the machine. This angle may, of course, be more or less than as shown. In order that the rolls shall act to feed longitudinally forward a billet gripped between them, they are skewed, being, as usual, set at different angles to a plane passing through the center line of feed of the billet. As shown, the axis of each roll is at an angle of about 6 to the horizontal plane extending through the center line of feed of the billet, one above and one below this horizontal plane. This angle also may, of course, be more or less than 6. The usual billet guides 12, shown in Fig. 3, and the usual piercing point, or mandrel, shown by dotted lines at 13 in Fig. 1, and mandrel rod and guiding means therefor are provided. The billet 14, guided and advanced endwise to enter its forward end between the rolls, is gripped by the rolls and compressed and rotated and drawn forward by the rolls between the guides 12 to force the metal over the mandrel point, thus forming the tube or hollow in the usual way.

Each of the rolls 10 and 11 is carried by a shaft 15 mounted in bearings 16 on a support 17. The support 1'? for each roll shaft rests at its forward end on a bed casting 18 which extends crosswise of the machine, and toward its rear end the support 17 drops downwardly and is widened out to provide a base portion 19 which rests on a bed casting 20 and which provides a support for the driving motor. The casting 18 and the two castings 20 rest on and are secured to beams 21 and 22, respectively, which in turn are connected, so that a bed for the entire machine is formed by the beams 21 and 22 and the castings 18 and 20.

The driving motors 25 and 26, one for each of the rolls, are mounted on the base portions 19 of the supports 17 and have their shafts 15-a connected directly to the respective roll shafts 15 through couplings 2'7. By connecting the motors directly to the roll shafts, all gearing between the motor and the roll shaft is avoided and friction losses thus reduced. In order to permit of such direct connection of the motors without having to use motors of prohibitive size and weight, the rolls are, as shown, made of relatively small diameter and driven at relatively high speed.

The diameter of the rolls may, of course, vary widely, but I have found that conical rolls of substantially the shape shown having a diameter of about12 driven at from 1'70 to 300 R.P.M. may be used for piercing billets up to at least 3 or 4" in diameter in place of substantially larger rolls driven at lower speed, without loss in efiiciency or in the quality of the work. Such small diameter rolls are driven at an increased R.P.M. in order to give a suitable surface speed to their working faces, most desirably somewhat greater than the surface speed of the larger rolls heretofore used driven at the speed at which such larger rolls have usually been driven. The rotation speed is thus increased so that it becomes entirely practical to drive the rolls by directconnected D.C. electric motors.

Each support 1'? is pivotally connected to its bed casting 20 by means of a pin 28 and rests at its front end on a bearing surface of the supporting casting 18 on which it may slide when the support is moved about its pivot to carry its roll toward or away from the other roll. The forward end of each of the supports 17 is secured in adjusted position on the casting 18 by means of bolts 30 which extend through curved slots 31 formed in the top of the casting, these slots be ing on. arcs struck from the center of the pivot tending through curved slots 33 in the top of the casting 20 so as to permit turning movement of the support 17 about its pivot pin when the nuts of the bolts 32 are loosened.

For moving the rolls toward or from each other and adjusting the distance between the rolls when in operative position and for additionally holding the roll supports 17 against the pressure on the rolls when the mill is in operation, a threaded thrust rod 35 is provided for each support 17 ex tending through a threaded opening in a bracket 36 bolted to the end of the bed-casting 18. The inner end of this rod is provided with a head 37 which is held in a yoke 38 attached to the side of the support 17. The yoke 38 is preferably positioned opposite the axis of the roll shaft and close to the roll end of the shaft. A lock-nut 39 serves to lock the rod 35 in any desired position of adjustment. and 32 of either support 17 are loosened, the support, carrying the motor and the roll shaft, may

be turned about its pivot pin 28 by turning the screw rod 35 to move the roll 10 or 11 toward or away from its cooperating roll. The rolls may thus be readily moved apart when desired for any reason, as, for instance, when a piercing point becomes jammed in a billet, and may readily be moved back to their operative position. Similarly, the distance between the rolls may readily be changed and adjusted as desired.

An ammeter 40, shown diagrammatically in Fig. 4, is provided in the supply circuit of each motor to serve as a load indicator, showing the load on the motor and, therefore, the torque resistance of the roll driven by the motor and approximately the work being done by the roll. Each motor is also provided with speed adjusting or controlling means, which in the case of compound wound electric motors will most desirably be an adjustable resistance 41 in the circuit to the shunt field winding 42, as shown in Fig. 4.

Speed indicators are also most desirably provided for showing the speed at which each roll is being driven. For this purpose, there may be provided for each roll, as shown in Fig. 3, a magneto-generator 43 driven by the motor shaft 15-11 and a voltmeter 44 connected in the magneto-generator circuit and having its scale cali brated to read in revolutions per minute. The load indicating ammeters 40, the speed-controlling adjustable resistance devices 41, and the speed-indicating voltmeters 44 for both motors may conveniently be mounted on a panel 45, as

-shown diagrammatically in Fig. 4, arid the circuit connections may be as shown in this figure.

In order to provide for automatic adjustment of the speed at which the individual rolls are driven to compensate for a difference in slip of the rolls due to condition of the roll surfaces or other cause and to equalize to a degree the work being done by the individual rolls, the driving motors are, as stated, most desirably compound wound direct current motors having a considerable drooping speed-torque characteristic. With such motors, if one of the rolls is doing less work than the other and, therefore, consuming. less power, the motor driving that roll will automatically speed up and the increased speed of the roll will result, as before stated, in an increase in the work done thereby.

It is not desirable to use motors having such a high drooping characteristic as would maintain full equalization of load between the two motors, since the no-load speed of such motors would be so much higher than the full-load speed that When the nuts on the bolts 30- undesirable shock and heavy strain would result when the billet enters between the rolls, and it would also mean a very heavy and undesirable current rush atthe instant of the load coming on the motors. With a limited but substantial drooping characteristic which does not involve such difference between the no-load and fullload speeds as would have to a harmful degree the disadvantages stated, the equalization, although only one of degree, is still very effective, and loss in efliciency of the mill, which would otherwise result from a difference in slip of the individual rolls on the work, for example, is to a considerable extent overcome. The motors should, therefore, have, most desirably, such a limited droop ing characteristic.

Even when the mill is provided with means for automatically varying the relative roll speeds in the direction of equalization of work done, it is usually desirable to provide also means for adjusting the relative speed of the rolls manually, or at will. Most desirably, especially when an independent driving motor is provided for each roll, a separate speed adjusting or controlling means is provided for independently varying the speed of each roll.

The load indicating means for each roll and motor unit is of special importance in connection with the manual speed adjusting means, permitting the operator to observe the power being absorbed by each roll and to adjust the speed accordingly to compensate for differences in work done. There would, of course, also be an advantage in having the mill provided with such separate load indicators for each roll, even apart from the provision of means for manual adjustment of the relative speed of the rolls, since the on the billet more than the other, the motors will preliminarily be adjusted to drive the two rolls at equal speeds. Then if in the operation of the mill one roll should slip on the work more than the other, the torque resistance on the motor driving the slipping roll will be less than the torque resistance on the other motor, and the motor driving the slipping roll will automatically speed up to take more nearly its share of the load, and the other motor will drop slightly in speed, the relative speed of the rolls being thus automatically adjusted in the direction of equalization of load on. the motors and equalization of the work being done by the rolls. Because of the limited drooping speed-torque characteristic of the motors, the equalization of load on the motors will. not be complete and a difference in load will be indicated by the ammeters, and the difierence in speed at which the rolls are being driven will be indicated by the speed indicating volt meters.

If the motors, instead of being compound wound D. C. motors giving automatic speed of adjustment, were straight shunt wound motors, the difference in work being done by the motors would then be shown by the ammeters, indicating difference in torque resistance and work done by the rolls, and adjustment of the relative speed of the motors in the direction of equalization of torque resistance and of work being done by the rolls would be effected by manual adjustment of one or both of the adjustable resistance devices 41. And even when motors which have the property of automatic adjustment toward constant power are used, manual adjustment of the speed at which the rolls are driven, by means of the resistance devices 41, may with advantage be resorted to for the purpose of securing a more complete equalization of the loads on the two motors and, consequently, of the work being done by the two rolls. Such use of the manually adjustable speed controlling means for supplementing the automatic speed control provided by the use of motors which tend toward constant power is of special valuein cases where the rolls develop considerable difference in slippage on the work.

With some types of rolls, and especially with conical rolls, it is not always possible to have the two rolls of equal pitch diameter, and this is especially true in the use of rolls which have become worn and have been re-ground. The difference in the pitch diameters of rolls driven at equal speed means a difference in surface speed of the rolls which is sometimes sufficient to put the mill considerably out of balance. Speed adjustment of the rolls according to the present invention serves for readily correcting such a condition. If the rolls are known to be of unequal diameters, or if they are known to have engaging surfaces of unequal degrees of smoothness or otherwise of such character that one will slip on the work more than the other, the motor speeds may be, and desirably will be, suitably adjusted by means of the resistance devices 41 to compensate for such difference before the mill is put in operation.

The term compensate is used in the claims to include the effecting of partial compensation.

What is claimed is:

1. The method of piercing metal billets, which comprises compressing, cross-rolling and advancing the billet between driven rolls, and adjusting the relative speed of rotation of the rolls to reduce a difference in work done by the individual rolls resulting from a difference in slip of the rolls on the workby increasing the relative speed of the roll which has the greater slip to cause such roll to have a greater surface speed than the other roll or rolls.

2. The method of piercing metal billets, which comprises entering the billet endwise between driven rolls by which it is compressed and crossrolled and the metal advanced over a piercing mandrel, and driving a roll which has a greater tendency to slip on the work than the other roll or rolls at a relatively higher surface speed to increase the work done by that roll.

3. The method of piercing metal billets, which comprises entering the billet endwise between driven rolls by which it is compressed and crossrolled and the metal advanced over a piercing mandrel, and adjusting the relative speed of rotation of the rolls while the mill is in operation to reduce a difference in work being done by the rolls by increasing the relative speed of a roll which is slipping on the work more than the other roll or rolls to cause such roll to have a greater surface speed than the other roll or rolls.

4. The method of operating a cross-rolling piercing mill having driven skewed rolls, which comprises observing the power absorbed by the individual rolls, and increasing the relative speed of rotation of a roll which is taking less power than the other or others to cause such roll to have a greater surface speed than the other or others and thereby to increase the work done by that roll.

5. The method of increasing the efficiency of a cross-rolling piercing mill having driven rolls one of which is smoother than another, which comprises driving the smoother roll at a higher surface speed than the other.

6. The method of operating a cross-rolling piercing mill, which comprises operating the mill with the rolls driven at substantially equal surface speeds, and thereafter from time to time adjusting the relative speed of the rolls to compensate for differences in slip of the individual rolls on the work by increasing the relative speed of a roll which is slipping on the work more than the other roll or rolls to increase the proportion of work done by that roll.

7. The method of operating a cross-rolling piercing mill, which comprises adjusting the relative speed of rotation of the rolls to compensate for a difference in diameter of the rolls, and thereafter adjusting the relative speed of rotation of the rolls to compensate for differences in slip of the individual rolls on the work by increasing the relative surface speed of a roll which'is showing the greatest degree of slippage on the work to increase the proportion of work done by that roll.

8. A tube piercing mill, comprising a pair of divergent roll shafts, bearings for said shafts, conical piercing rolls on the adjacent ends of said shafts, a motor for independently driving each of said shafts connected to the end thereof remote from the roll, a separate support for the bearings and motor of each shaft, each support being mounted to turn about a vertical axis adjacent to the motor carried thereby for moving the piercing roll carried by the shaft mounted thereon toward and from the other roll, adjusting means for turning said supports about their pivotal axes, and locking means for securing the supportsagainst turning movement.

9. A tube piercing mill, comprising a pair of divergent roll shafts, bearings for said shafts, small conical piercing rolls on the adjacent ends of said shafts, a D, C. electric motor for independently driving each of said shafts directconnected to the end thereof remote from the roll, a separate support for the bearings and motor of each shaft, each support being mounted to turn about a vertical axis adjacent to the motor carried thereby for moving the piercing roll carried by the shaft mounted thereon toward and from the other roll, adjusting means for turning said supports about their pivotal axes, and locking means for securing the supports against turning movement.

10. A tube piercing mill, comprising a pair of divergent roll shafts, bearings for said shafts, conical piercing rolls on the adjacent ends of said shafts, means for applying driving force .to the ends of said shafts remote from the rolls, a separate support for the bearings of each shaft, each support being mounted to turn about a vertical axis adjacent to the end of the shaft remote from the roll for moving the roll carried by the shaft mounted thereon toward and from the other roll, adjusting means for turning said supports about their pivotal axes, and locking means for securing the supports against turning movement.

HEBER C. INSLEE. 

